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Liquid biopsy offers option for EGFR testing without lung tumor tissue
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Blood assays identified EGFR mutations in patients with advanced non-small cell lung cancer with insufficient tumor biopsies, according to a prospective analysis published in Annals of Oncology.
“The clinical benefits of tyrosine kinase inhibitors in stage IIIB to IV NSCLC patients carrying sensitizing mutations in the EGFR gene are well established, and EGFR testing in tumor tissue has become a routine clinical practice,” Miguel Angel Molina-Vila, BSc, PhD, laboratory director of Pangaea Oncology at Quirón Dexeus University Hospital in Barcelona, and colleagues wrote. “However, 5% to 20% of advanced NSCLC patients cannot be biopsied or the tumor tissue in biopsies or cytological samples is insufficient for successful genetic analysis.”
Studies have explored whether circulating-free DNA from serum or plasma of patients with advanced NSCLC can be used to reliably determine EGFR mutations. However, there have been no studies of patients treated with TKIs based only on a positive EGFR result in blood.
Molina-Vila and colleagues analyzed EGFR mutations in the circulating-free DNA of 1,138 patients with stage IIIB to stage IV NSCLC using a real-time polymerase chain reaction assay. Because no commercial kits were available at the time testing commenced, researchers developed and validated a PNA-Q-PCR assay for the detection of mutations in exons 19, 20 (p.T790M)
and 21 (p.L858R and p.L861Q).
“The assay is simple, not more expensive than tissue analysis, has a short turnaround time and its limits of detection, sensitivity (75.9%) and specificity (100%) are in the range of other reported methodologies,” the researchers wrote. “The main limitation of the assay is that it cannot detect the relatively infrequent mutations in exon 18 of EGFR.”
The goal of the study included to determine if this method may be used as a surrogate to select patients with no biopsy or insufficient tumor tissue for treatment with EGFR TKI therapy.
In total, 1,033 patients underwent prospective testing at disease presentation, of whom 1,026 were evaluable (men, 55.8%; former smokers, 46.8%). Of them, 113 (11%; women, 66.4%; never smokers, 63.7%) has a sensitizing mutation in circulating-free DNA, including 75 with exon 19 deletions and 38 with exon 21 point mutations.
Thirty-one patients were positive only in plasma and 11 in only in serum.
The researchers measured concentration of DNA using Qubit (Thermo Fisher Scientific) to evaluate the blood samples of a subset of patients with EGFR mutations (n = 40) and wild-type EGFR (n = 40). More than 60% of circulating-free DNA samples contained less than 10 pg mutant genomes/l.
Researchers then determined mutation load in 149 serum and plasma samples from 91 patients with EGFR mutations. More than 50% of samples contained less than 10 mutated genomes/µl with allelic fractions below 0.25%. Median mutation load appeared higher in plasma than serum samples (0.23% vs. 0.12%), and in samples positive for exon 19 compared with exon 21 deletions (0.26% vs. 0.07%).
In addition, 105 patients who progressed following EGFR TKI therapy also underwent prospective screening.
The assay detected sensitizing mutations in 56.2% of these patients and the p.T790M resistance mutation in 35.2%.
The researchers retrospectively collected clinical information from 18 patients treated with TKIs based exclusively on the results of the EGFR testing in blood.
Thirteen patients achieved a partial response for an overall response rate of 72%. Median PFS was 11 months.
Duration of response ranged from 5 months to 18 months in eight patients who had available data. Two patients who harbored a p.L858R mutation progressed after 5 and 8 months, whereas the duration of response range from 7 months to not reached in the six patients who harbored exon 19 mutations.
“Some of the patients identified as EGFR positive, based solely on the results of the PNA-Q-PCR assay, showed remarkable responses to targeted therapy,” Molina-Vila and colleagues wrote.
Although blood assays proved to be a feasible alternative to tumor biopsies, the researchers noted this method will not become the standard of care.
“’Liquid’ biopsies will never replace tumor biopsies, which constitute unique sources of information that cannot be obtained by any other means,” they wrote. “However, our results demonstrate that prospective EGFR analysis in blood can be used to select patients for TKI therapy when no tumor tissue is available for genetic testing.” – by Kristie L. Kahl
Disclosure: Molina-Vila reports he has no relevant financial disclosures. Please see the full study for a list of all other researchers’ relevant financial disclosures.
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